MySQL索引的完整教程(创建、查看、修改、删除与日常管理)

CREATE TABLE `openapi_apilog` (
  id BIGINT AUTO_INCREMENT COMMENT '主键',
  user_id VARCHAR(32) NOT NULL,
  date DATE NOT NULL,
  path VARCHAR(500) NOT NULL,
  login_ip VARCHAR(50),
  price DECIMAL(10,2),
  creat_time DATETIME,
  -- 主键索引
  PRIMARY KEY (`id`),
  -- 普通联合索引
  INDEX idx_user_date (user_id, date),
  -- 唯一索引
  UNIQUE INDEX uk_path_uid (path, user_id),
  -- 字符串前缀索引（path只截取前40字符建索引，节省空间）
  INDEX idx_path_prefix (path(40))
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT '接口日志表';

CREATE [UNIQUE] INDEX 索引名 ON 表名(字段1, 字段2...);

CREATE INDEX idx_user_id ON openapi_apilog(user_id);

CREATE INDEX idx_user_date_path ON openapi_apilog(user_id, date, path);

CREATE UNIQUE INDEX uk_verify_id ON openapi_apilog(verify_idf_id);

CREATE INDEX idx_path_prefix ON openapi_apilog(path(40));

CREATE INDEX idx_cover ON openapi_apilog(user_id, date, path, login_ip, price, creat_time);

-- 普通索引
ALTER TABLE openapi_apilog ADD INDEX idx_date (date);

-- 唯一索引
ALTER TABLE openapi_apilog ADD UNIQUE INDEX uk_ip (login_ip);

-- 主键索引（表无主键时添加）
ALTER TABLE openapi_apilog ADD PRIMARY KEY (`id`);

SHOW INDEX FROM openapi_apilog;

DESC openapi_apilog;

SELECT TABLE_NAME, INDEX_NAME, COLUMN_NAME, NON_UNIQUE
FROM INFORMATION_SCHEMA.STATISTICS
WHERE TABLE_SCHEMA = DATABASE()
ORDER BY TABLE_NAME, INDEX_NAME, SEQ_IN_INDEX;

SELECT * FROM sys.schema_unused_indexes;

EXPLAIN 
SELECT login_ip,price FROM openapi_apilog 
WHERE user_id='10001' AND date='2026-07-02';

-- 1. 删除旧索引
DROP INDEX idx_user_date ON openapi_apilog;
-- 2. 创建新索引
CREATE INDEX idx_user_date_time ON openapi_apilog(user_id, date, creat_time);

DROP INDEX idx_path_prefix ON openapi_apilog;

ALTER TABLE openapi_apilog DROP INDEX idx_user_date_path;

ALTER TABLE openapi_apilog DROP PRIMARY KEY;

OPTIMIZE TABLE openapi_apilog;

-- 区分度越接近1，索引效果越好
SELECT COUNT(DISTINCT user_id)/COUNT(*) FROM openapi_apilog;